1. Field of the Invention
This invention is concerned with a method of increasing the catalytic cycle length in methanol conversion catalysts by a combination of steaming and acid extraction. The acid-extraction step in accordance with the novel process of this invention requires the use of a crystalline aluminosilicate zeolite in a silica matrix.
2. Description of the Prior Art
The conversion of lower alcohols, including methanol, to various products such as gasoline, olefins, and/or distillates is an important area of technology which has been described in the patent and technical literature. The particularly advantageous catalysts which are utilized in the conversion of methanol are a special class of crystalline aluminosilicate zeolites having a silica-to-alumina ratio greater than 12 and a Constraint Index within the approximate range of 1 to 12. A typical material of this type is zeolite ZSM-5. There are many patents and publications which describe the conversion of methanol to hydrocarbons such as gasoline, olefins and/or distillates over said special zeolites including U.S. Pat. Nos. 3,931,349; 3,969,426; 3,899,544; 3,894,104; 3,904,916; 3,894,102; 4,025,576; 4,374,295; and 4,083,889; the disclosures of which are herein incorporated by reference. It is also known in the art that steaming under certain circumstances can enhance the activity of acid catalyzed reactions and such is disclosed in U.S. Pat. No. 4,326,994. It is also known that steaming can enhance the stability of zeolite catalysts for various acid catalyzed reactions as well as methanol conversion and such is disclosed and claimed in U.S. Pat. No. 4,429,176. It is also known in the art that treatment with phosphorus and/or steam can extend the life of an isomerization catalyst such as disclosed and claimed in U.S. Pat. No. 4,423,266.